Haze is a phenomenon that occurs when light is scattered inside or on the surface of a transparent sample, resulting in a cloud-like appearance. It is defined as the percentage of light that deviates from the direction of incident rays due to forward scattering when light transmittance passes through the sample. When the deviation between the transmitted light and the incident light is greater than 2.5°, it is generally qualified as haze. At this point, the luminous flux is regarded as haze.
Light transmittance, on the other hand, is the ratio of transmitted light to incident light. The commonly reported value is the percentage of transmitted light, which represents the proportion of the flux of light passing through the material.
The key point in describing haze is the presence of scattered light. When light shines on greenhouse glass, some of it will be reflected back (reflected light), some will be absorbed (absorption of light), and some will penetrate the material (transmitted light). Within the transmitted light, some will continue in the original propagation direction (parallel transmission), while another part will be internally scattered due to the material's characteristics. This scattered light is the focus of the definition of haze, distinguishing it from light transmittance.
In general, there is an inverse relationship between light transmittance and haze. Materials with high light transmittance tend to have low haze, and vice versa. For greenhouse glass, this relationship is exemplified by scattering glass, where high haze values result in large scattering angles, but not necessarily high light transmittance.
When purchasing greenhouse glass, it is important to consider both haze value and light transmittance separately.
The consideration standard for haze value begins with an assessment of the crops grown in the greenhouse. Different plants have varying light requirements, and local climate temperature differences also play a role in determining the appropriate haze level. For example, in areas with significant temperature differences, choosing high-haze glass can help balance the temperature impact on the greenhouse.
The contrast between glass with different haze values can be observed in the size of scattered light spots. Under the same conditions, glass with 75 haze has a scattered light spot size of 375mm, while glass with 20 haze has a spot size of 100mm. This difference directly impacts the light coverage area of the greenhouse.
The standard for light transmittance is based on achieving high levels of transmittance. Ordinary float glass has low light transmittance, which can impact the light requirements of greenhouse crops. Higher light transmittance leads to increased benefits for the greenhouse, allowing crops to grow under conditions closer to those of open air. Additionally, high light transmittance can help balance adverse effects such as excessively high temperatures.
Currently, the highest light transmittance available on the market is 97.5% for blue-violet light (with different values for infrared light). Recommended types of greenhouse glass include diffuse scattering glass, diffuse reflection(AR coating) glass, and anti-reflection glass. These options possess characteristics such as haze, scattering, and high light transmission.
In recent years, experiments and planting comparisons have shown that haze and scattering play crucial roles in the growth of greenhouse crops. The use of glass with these properties has resulted in approximately 20% higher planting efficiency compared to ordinary glass.
For further details on these topics, please refer to previous content regarding scattering tempered glass, greenhouse glass standards, and the distinguishing features of different types of glass commonly used in greenhouses.
In conclusion, understanding the concepts of haze and light transmittance is essential when selecting greenhouse glass. By considering the specific needs of the crops and the local climate conditions, it is possible to make informed decisions that optimize the growth environment for greenhouse cultivation.
